Decent HF-VHF indoor antenna

Discuss commercial and home made antennas.
Post Reply
X3nus
Posts: 7
Joined: Thu Jun 30, 2016 7:05 pm

Decent HF-VHF indoor antenna

Post by X3nus » Thu Jun 30, 2016 7:17 pm

Hi everyone! I’m a beginner in SDR radios and currently find a lot of fun in scanning radio frequencies to find and identify various types of signals. Problem is - I'm living on a first floor in a city block, so I can't constantly place an indoor antenna outside, and therefore cannot make a full-sized antenna for receiving shortwave as well. That’s why I’m searching for a decent commercial indoor antenna to effectively cover the HF-VHF range which can be easily set it up near the window for scanning all mentioned frequencies with the ability to receive weak signals better.
There are many recommendations for a discone as a universal antenna, I’ve even found some indoor desktop versions of it (like this one, for example), but as far as I know they can't receive HF signals well, so it is probably not a good choice.
So far I've managed to find this antenna: MFJ-1022. Its nominal frequency range looks perfect, but looking at its short 50 cm telescopic antenna I have doubts that it actually can receive HF signals well. Also it's an active antenna, but does the amplifier actually help in a noisy indoor environment which is also surrounded by buildings from all sides? Also I've tried to find any decent indoor magnetic loop antenna since they are claimed to have better noise protection, but most of them cover very narrow band, and those having a good frequency coverage (like this, for example) are very pricey. Maybe you can suggest a cheaper one?
P.S. Currently I have a simple self-made indoor loop antenna made out of a coaxial cable fixed around a window frame (a really simple setup with no variable capacitor, filters or anything) and a bundled telescopic antenna from rtl-sdr.com dongle. As you can see, both of my antennas are very simple, so any help in finding something better and universal than those two will be much appreciated.

rtlsdrblog
Site Admin
Posts: 2330
Joined: Mon Nov 19, 2012 11:54 pm

Re: Decent HF-VHF indoor antenna

Post by rtlsdrblog » Thu Jun 30, 2016 10:05 pm

Indoor is tricky as you'll be picking up a lot of interference from electronic devices inside. So an amplified antenna probably won't be that great as it will only increase the amount of noise picked up too. I'd recommend two different antennas, one for HF and one for VHF+.

Are you able to stick anything out your window? To start i'd simply build a quarter wave ground plane or buy a discone and get it out the window on an arm. For HF a magnetic loop would be good for your situation. Or you could try and inconspicuously run a thin long wire antenna down from your roof.

The AN-LP1 loop is pretty cheap, but mainly covers only shortwave frequencies and not ham ones, though you might still get some coming in. But you'll need to stick that out the window too to get it away from indoor noise for best results.

X3nus
Posts: 7
Joined: Thu Jun 30, 2016 7:05 pm

Re: Decent HF-VHF indoor antenna

Post by X3nus » Fri Jul 01, 2016 6:45 pm

Thank you for your answer and suggestions! Unfortunately I can’t actually stick an arm with a massive antenna outside, the only thing I can do is to mount a small sized antenna with a magnetic base to the metal ramp of my window for a short time. I’ve tried it with my telescopic antenna from the dongle, and when placed outside it definitely performed better in VHF than the indoor self-made magnetic loop, but it can't receive much below the FM band and should be taken back from outside every time.
The indoor loop described above and made just from a piece of 50 ohm satellite TV coaxial cable performed better in VHF than the telescopic antenna when placed on the windowsill, and works pretty well in shortwave. I’ve tested it with the Airspy mini and the Spyverter, compared it to this online SDR and found that using the decimation helps to hear most of the international broadcasts (I’ve even heard a lot of hams from within a 800 km radius on 3 mhz), and even with the maximum gain in Airspy settings the noise floor is around -45dB. Still it can’t get really weak signals; also there are a lot of noise and spikes of interference everywhere and no signals below 2 mhz.
A long wire from the roof is definitely a thing to try. The only thing I can’t understand… The MFJ makes a line of indoor shortwave antennas (like the one I’ve mentioned above, or more advanced like this), which are basically preselectors\amplifiers for a simple wire antenna – and all of them are supplied (and intended to work) with the same 50 cm telescopic antenna. How are such antennas supposed to effectively receive signals with the wavelengths of tens of meters with such a small telescopic rod?

rtlsdrblog
Site Admin
Posts: 2330
Joined: Mon Nov 19, 2012 11:54 pm

Re: Decent HF-VHF indoor antenna

Post by rtlsdrblog » Sat Jul 02, 2016 12:53 am

They are "electrically short active antennas". Basically although the length is all wrong and so resonance is naturally way off, but the electronics inside match and correct for this and make it look like a 50 ohm antenna to the radio, giving good SWR. Still not as good as a proper sized antenna, but much better than without the active part.

X3nus
Posts: 7
Joined: Thu Jun 30, 2016 7:05 pm

Re: Decent HF-VHF indoor antenna

Post by X3nus » Sat Jul 02, 2016 6:14 pm

Thank you again for the explanation! :)

j4zz
Posts: 2
Joined: Wed Jul 13, 2016 10:57 am

Re: Decent HF-VHF indoor antenna

Post by j4zz » Wed Jul 13, 2016 11:21 am

I try to not create other thread,..:)

I got SDR dongle (said; HF and U/VHF ) from eBay last night. I stayed in 9th floor apartment (around 45 meter height)
Installed SDR Sharp on my laptop, on VHF I can hear local FM radio but no on HF(I hear qrm only). I use antenna that came with the dongle, put in window(indoor).

For HF , thinking to make dipole (or quad) antenna and put/tape into along window frame, question do I need balun for this kind receiver antenna?

~ron~

rtlsdrblog
Site Admin
Posts: 2330
Joined: Mon Nov 19, 2012 11:54 pm

Re: Decent HF-VHF indoor antenna

Post by rtlsdrblog » Thu Jul 14, 2016 12:53 am

Since you have that receiver, did you ensure that you set the software to use the direct sampling "Q-branch" when you were listening to HF?

Also, the supplied antenna that comes with those units is probably next to useless on HF. You really need a longer antenna like a long wire for HF, or you may get nothing.

j4zz
Posts: 2
Joined: Wed Jul 13, 2016 10:57 am

Re: Decent HF-VHF indoor antenna

Post by j4zz » Fri Jul 15, 2016 9:50 am

rtlsdrblog wrote:Since you have that receiver, did you ensure that you set the software to use the direct sampling "Q-branch" when you were listening to HF?

Also, the supplied antenna that comes with those units is probably next to useless on HF. You really need a longer antenna like a long wire for HF, or you may get nothing.
Thanks for your input

Post Reply